Hi Frank,

> After switching the instrumen off and back on about two weeks ago,
> the CO2  showed a broad tailing, resulting in wrong results
> for 13C/12 C in standards and also too low measured C -
> concentrations. The N2 peak seems perfectly o.k., concentrations and
> isotope ratios. I have changed the O2 and carrier flow rates in all
> directions, put on new oxidation and reduction columns, renewed  the
> Anhydron water trap - but, alas, to no avail...
>
> Is it possible the chromatographic column needs to be changed (the
> instrument has done about 10000 measurements).

In theory (theory being the operative word here), the column
shouldn't go off. However, you might still end up replacing your
column.

I know it's rather obvious and you have checked it probably already
but is your column at the right temperature? In our system, the
column furnace (heater) doesn't take too kindly to interruptions of
the power supply whether intentional or due to a power failure.

Second possibility, the stationary phase (or its packing rather) of
your column has been disrupted. This is more likely caused by
sudden changes in carrier gas flow and pressure. In this case you
will have to replace the column or repack it yourself.

By the by, what does you CO2 reference signal look like? Crisp
and sharp or is it tailing too?

Hope this proves helpful.


Best wishes,
                        Wolfram



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Dr. W. Meier-Augenstein, CChem MRSC
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University of Dundee, Dept. of Anatomy & Physiology,
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